Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section.
There has been known the following image reading apparatus. The image reading apparatus irradiates a document with light from a light source. Light receiving elements receive the reflected light to read image data on the document. This image reading apparatus reads the image data at a uniform print density regardless of unevenness in sensitivity of the light receiving elements and a variation in amount of light of the light source. Therefore, reading a white reference member using respective light receiving elements acquires white reference data. A plurality of positions of the white reference member are read, and an averaging process is performed on a plurality of pieces of data acquired by these respective light receiving elements. Thus, the white reference data is acquired. This reduces an influence of variation in print density or a similar variation of the white reference member itself, ensuring acquiring appropriate white reference data.
However, it is difficult to acquire the sufficiently appropriate white reference data only by performing the above-described averaging process on the plurality of pieces of data. Accordingly, the following method has been known. If the plurality of pieces of data include abnormal data, the abnormal data is excluded and then the averaging process is performed. Thus, further appropriate white reference data is acquired. Additionally, a method that sorts the white reference data and then excludes the abnormal data from the white reference data has also been known.